The invention concerns equipment and a method for making a needle-fin tube, and a needle-fin tube.
It is characteristic of indirect heat transfer and cooling systems that the operating temperature of the liquid circulating in the liquid circulation network will drop below zero Celsius degrees. A mixture of water and some agent preventing the water from freezing is hereby often used as the heat carrier liquid. Mono-ethylene glycol and mono-propylene glycol are the anti-freeze agents most frequently used. With an increasing content of anti-freeze agent and a lowering temperature, the flow in the smooth tube will easily be laminar, whereby the heat transfer coefficient between the liquid and the tube surface is low and the thermal resistance is hereby high. As a result of this the value of the heat delivery surface's coefficient of thermal transmittance remains small, which can be compensated for by increasing the heat delivery surface area or, on the other hand, steps can be taken to improve the value of the heat transfer coefficient of the liquid side.
As a solution to improve the heat transfer coefficient of the liquid side a turbulator wire is used, which is installed inside the tube (a passive method for boosting the heat transfer), owing to which the flow is made turbulent even at low flow velocity values, and the heat transfer is thus made more efficient.